Debugging withdrawToken Fuzz Fail — Getting UnsupportedToken() Instead of Patrick's Errors

[successaje]

Hey everyone 👋

I'm currently on Section 5: TSwap of Patrick's course, specifically the "Debugging Fuzz Sequences" part. While following along, Patrick gets errors like ERC20InsufficientAllowance or ERC20InsufficientBalance.

However, when I run the invariant test, I get:

[FAIL: HandlerStatefulFuzzCatches__UnsupportedToken()]
[Sequence] (original: 15, shrunk: 1)
sender=0x0000000000000000000061640518cc99E3DFBd66
calldata=withdrawToken(address)
args=[0x0000000000000000000061640518cc99E3DFBd66]

It seems my test is hitting a revert due to an unsupported token. Could this be because my yieldToken contract doesn't recognize the token address being passed? Or maybe I didn't properly set the targetContract to the handler?

Just wondering if anyone else ran into this before or if I'm missing a setup step here. Appreciate any help!

[EngrPips]

Hey @successaje, it seems like you did everything correctly. Please run forge clean, delete your cache folder, run foundryup, and then retry the test. Let's see if that makes any difference.

[successaje]

Thanks @EngrPips, I ran the cleanup steps but still got the same error:

Failing tests: Encountered 1 failing test in test/invariant-break-2/Handler/Invariant.t.sol:Invariant [FAIL: HandlerStatefulFuzzCatches__UnsupportedToken()] [Sequence] (original: 3, shrunk: 1) sender=0x0000000000000000000028Df147a6E385ECAf815 addr=[src/invariant-break/HandlerStatefulFuzzCatches.sol:HandlerStatefulFuzzCatches]0x04da53e337F3b042A2cAAB9875002F50D11Febb5 calldata=withdrawToken(address) args=[0x0000000000000000000000000000000000000c65] statefulFuzz_testInvariantBreaksHandler() (runs: 0, calls: 0, reverts: 1)

The fuzzing engine is definitely calling withdrawToken() with a random token address that isn't in the supported list, which causes the UnsupportedToken() revert. I think the handler should maybe ignore unsupported tokens them out based on the implmentation.

[EngrPips]

It shows in your Handler contract that you hardcoded the token to withdraw to be the token you have passed in to the Handler contract which are also the token that you have set as the supportedTokens on the implementation contract so I don't understand how come the implementation contract is being called with a random token address.

[EngrPips]

Hello @successaje, you are running into that error because you set your target-contract wrongly. It should be set to the Handler contract and not the hsfc contract as you have it in your Invariant contract.

So change targetContract(address(hsfc)) to targetContract(address(handler)); and the test process should run as expected.

[EngrPips]

You should also run forge clean and delete the cache folder before you run a new process so that Foundry does not run with the cached information.

[successaje]

You're absolutely right, that was it.

Thanks so much @EngrPips, changing targetContract(address(hsfc)) to targetContract(address(handler)) fixed the issue completely.

Really appreciate your help in pointing that out! 🙏

[EngrPips]

I am glad you figured it out. Keep crushing it.